source: http://www.securityfocus.com/bid/954/info

Firewall-1 includes the ability to alter script tags in HTML pages before passing them to the client's browser. This alteration invalidates the tag, rendering the script unexecutable by the browser. In version 3, this function can be bypassed by adding an extra opening angle bracket. The tag will be left unmodified, and the browser will be able to execute the contained script. Hostile script could lead to a remote compromise of the client system.

Firewall-1 version 4 will alter the tag as expected. 

<html>
<<script language="javascript">
alert("<<script> tag succesfully passed!")
</script>
Click <A HREF="/vdb/bottom.html?section=exploit&vid=954">here</A> to return to vulnerability listing.
</html>